The present invention is generally related to polymeric films and coatings. More particularly, this invention is related to polymerized di-p-xylylene films and coatings, including apparatus and methods for making the same.
It is well known to form films and coatings by pyrolysis and condensation polymerization of di-p-xylylene, which is represented by the structure: ##STR1##
In accordance with the established methods, powdered di-p-xylylene is sublimed at 150.degree. to 200.degree. C. and subsequently pyrolyzed in the gaseous state by heating the sublimed vapor to a temperature of approximately 450.degree. to 700.degree. C. Pyrolysis results in the splitting of the dimer to form the p-xylylene diradical, which is represented by the formula .H.sub.2 C--AR--CH.sub.2.. The diradical monomer is condensable onto a substrate to form a p-xylylene polymer, or poly-p-xylylene, which is a tough, strong and chemically inert film. Depending on the application, the film may be removed from the substrate and used for any desired purpose, or it may be left on the substrate as a protective coating. The polymeric film is commercially available from Union Carbide Corporation under the trademark Parylene. Very thin films of this type, on the order of a micron or less in thickness, are called pellicles.
The process described above can also be applied to the mono- and di-chlorinated di-p-xylylenes to produce chlorinated poly-p-xylylenes, which have slightly different chemical and physical properties making them more or less desirable in specific applications.
The poly-p-xylylene films and coatings are commonly used in optical applications and in the fabrication and protection of electronic components. Additionally, these materials are being used at the Los Alamos National Laboratory in the fabrication of laser fusion targets, which take the form of microscopic spheres containing mixtures of deuterium and tritium. For the latter purpose, it is occasionally necessary to form poly-p-xylylene coatings which are chemically inert, thermally stable at elevated temperatures, and sufficiently hard to permit machining of the polymeric coating into various desired shapes. Commercially available and other previously known poly-p-xylylene polymers have not met these requirements.